Prior to the present invention various methods were employed to synthesize bisphenols, such as bisphenol-A, by effecting reaction between a ketone and a phenol. One procedure, for example, involved the use of large amounts of inorganic acid catalysts, such as sulfuric acid or hydrochloric acid. Experience has shown, however, that the use of inorganic acids requires a means to neutralize such acids at the end of the reaction due to the corrosive action of the strong acids. In addition, distillation of the resulting bisphenol was often required because of the many by-products formed during the reaction under high acid conditions.
An improved procedure was developed by using a solid resin cation-exchange catalyst to effect the condensation between the phenol and the ketone. However, the disadvantage of the ion-exchange catalyst is the low acid concentration it provides resulting in the need for a rate accelerator such as a mercaptan. One procedure is shown by Apel et al, U.S. Pat. No. 3,153,001, which incorporates the mercaptan by partial neutralization of the ion-exchange catalyst in the form of a sulfonated insoluble polystyrene resin. Another procedure involves the partial esterification of such sulfonic acid moiety with an alkyl mercapto alcohol, as shown by McNutt et al, U.S. Pat. No. 1,183,564. A further procedure is shown by Wagner et al, U.S. Pat. No. 3,172,916, based on the partial reduction of the sulfonic acid to afford thiophenol functional groups. It has been found, however, that Wagner et al does not afford a particularly active type of promoter for synthesizing bisphenols, such as bisphenol-A, while the methods of Apel et al and McNutt et al are susceptible to chemical degradation.